The hot isostatic forming press (hereinafter referred to simply as "HIP machine") is usually provided with a holder frame for supporting the axial force of a high pressure container during HIP process, the holder frame being mounted swingably about a vertical axis to facilitate loading and unloading of work into and out of the high pressure container and at the same time for the sake of compactness in construction, as disclosed in U.S. Pat. No. 4,484,881.
As shown in Prior Art FIGS. 3 to 5, the HIP machine of the just-mentioned publication has a base plate 8 securely fixed to one side of a panel body 7 which mounts thereon pressure gauges 1, compressor 2, automatic valves 3, indicator lamps 4, manual valves 5 and press button switches 6. A high pressure container 10 is mounted on the base plate 8 through a bracket 9, and a press frame 11 which serves to support the axial force of the high pressure container 10 during HIP process is pivotally mounted on the same side of the base plate through hinges 12 for pivoting movements about a vertical axis 13 toward and away from the high pressure container 10. In addition to internally provided heat insulator and heater, the high pressure container 10 has upper and lower closure plugs 15 and 16 in its upper and lower openings to be opened at the time of loading and unloading work.
In a HIP machine of this sort, the holder frame 11 is brought into a holding position where it is mechanically engaged with the upper and lower plugs 15 and 16 of the high pressure container to support the axial force of the latter during the HIP process. In this position, the holder frame is locked in position by pins or hooks which are put into or out of locking position manually by an operator. Therefore, even if the high pressure container is filled with a gas, the pins or hooks can be removed to disengage the holder frame 11 from the high pressure container 10 as long as the gas pressure is at a low level, namely, as long as the axial force is small.
However, it is often the case that a processing gas of several atmospheric pressures remains in the container 10 even after the processing gas has been released from the container at the end of a cycle of HIP operation. It follows that, if the holder frame 11 is removed inadvertently in such a case, there might be a danger of the upper and lower plugs being blown off by the gas pressure.
Further, the high pressure container 10 is usually filled with a pressurized inert gas of 2-3 kgf/cm.sup.2 to prevent corrosion during a rest period between termination of a HIP operation and initiation of a next operation. Accordingly, the holder frame has to be held in the locking position even during the rest period by manually applying the pins or hooks, but a dangerous accident may incur by negligence on the part of the operator.